1. Field of Invention
This invention relates to a polymeric composition. More particularly, this invention relates to a thermoplastic polyester resin composition.
2. Prior Art
The use of thermoplastic polyesters such as the poly(alkylene terephthalates) in various applications is, of course, well known in the prior art. Such polymers are particularly useful in the preparation of molded structures. In general, the molded structures may be prepared via injection molding, compression molding, transfer molding and the like. Depending upon the particular end use, the thermoplastic polyester may be combined with other polymers, oils, fillers, reinforcing agents, antioxidants, stabilizers, fire retardants, antiblocking agents and the like.
In general, products fashioned with thermoplastic polyester resins exhibit good rigidity, heat resistance and electrical characteristics. The molded products do not, however, generally exhibit good impact resistance. As a result, polymeric compositions comprising a thermoplastic polyester as the sole polymeric component frequently cannot effectively be used in the preparation of many molded products. Moreover, the poor impact strength has, to some extent at least, restricted the use of such polymer compositions in other end use applications.
Heretofore, several techniques have been proposed for improving the impact resistance of shaped articles fashioned from a thermoplastic polyester. In general, these methods involve the incorporation of an elastomeric polymer into a polymeric composition comprising the thermoplastic polyester. In this regard, block copolymers comprising at least one monoalkenyl aromatic hydrocarbon polymer block and at least one conjugated diolefin polymer block are known to improve the impact strength of thermoplastic polyester resin composition products. Frequently, the conjugated diolefin block will be selectively hydrogenated so as to improve weatherability and heat resistance. The elastomeric block copolymer may be incorporated so as to form an interlocking network as taught in U.S. Pat. No. 4,101,605. The block copolymer may also, in effect, simply be admixed with the thermoplastic polyester as taught in U.S. Pat. No. 4,220,735. The block copolymer may further be modified by grafting an unsaturated carboxylic acid or a derivative thereof onto the block copolymer before physically admixing the same with the polyester as taught in U.S. Pat. No. 4,657,970 and International Kokai Application No. WO83/00492. The thermoplastic polyester resin compositions obtained via physical admixture of the components are, however, frequently, not stable and phase separation often occurs between the polyester and the block copolymer. Moreover, while the improvement in impact resistance realized with any of these systems may occasionally be significant, the improvement is more generally marginal and less significant. There is, of course, no known way to control these systems so as to insure a significant improvement in the impact resistance of the polyester composition.
It is, of course, known in the prior art that polymer compositions comprising an impact modifier will consist of at least two distinct phases-a first phase comprising the principle polymer and a second phase comprising the impact modifier. Heretofore, it has been believed that the interfacial adhesion between these two phases as well as the phase size of the second, impact modifier, phase were the principle variables affecting the extent of impact modification in such compositions. With any given polymer systems, there is, of course, little control over the interfacial adhesion between these phases although the amount of modifier actually used as well as the number of functional groups contained therein can be varied with some degree of accuracy. Similarly, there is little control over phase size of the second, impact modifier, phase although certain polymer properties believed to affect phase size such as molecular weight as well as the method used to prepare the polymeric blend can be varied with some degree of accuracy.
While, as indicated supra, the incorporation of an elastomeric block copolymer or a modified derivative thereof into a thermoplastic polyester resin composition frequently leads to the production of a product having improved impact strength, the extent of impact resistance improvement is, at best, difficult to control and, as a result, the amount of block copolymer, impact modifier, actually used or required to realize significant improvement is frequently relatively excessive. The improved impact resistance is, then, frequently obtained at the expense of other desirable properties characteristic of thermoplastic polyester resin products. Moreover, the selectively hydrogenated block copolymers are relatively expensive. As a result, even when the selectively hydrogenated block copolymers are used as a modifier in a thermoplastic polyester resin composition, they frequently are not used at a high enough concentration to yield a maximum impact strength. The need, then, for an improved impact modifiers which will be effective at lower concentrations, not subject to phase separation and affort better control over the extent of the impact improvement realized in thermoplastic polyester resin compositions is believed to be readily apparent.